Direct synthesis of catalyzed hydride compounds

ABSTRACT

A method is disclosed for directly preparing alkali metal aluminum hydrides such as NaAlH 4  and Na 3 AlH 6  from either the alkali metal or its hydride, and aluminum. The hydride thus prepared is doped with a small portion of a transition metal catalyst compound, such as TiCl 3 , TiF 3 , or a mixture of these materials, in order to render them reversibly hydridable. The process provides for mechanically mixing the dry reagents under an inert atmosphere followed by charging the mixed materials with high pressure hydrogen while heating the mixture to about 125° C. The method is relatively simple and inexpensive and provides reversible hydride compounds which are free of the usual contamination introduced by prior art wet chemical methods.

[0001] The United States Government has rights in this inventionpursuant to Contract No. DE-AC04-94AL85000 between the United StatesDepartment of Energy and Sandia Corporation, for the operation of theSandia National Laboratories.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] This invention relates to a method of producing a catalyzedalkali metal-aluminum hydride.

[0004] 2. Background Art

[0005] Alkali metals (lithium, sodium and potassium) form a wide varietyof simple hydrides and complex intermetallic hydrides that are commonlyused as reducing agents in various processes of organic chemistry. Whilesimple alkali earth hydrides may be produced by direct reaction betweenmolten alkali metal and hydrogen (at very high pressures andtemperatures) preparation of the more complex hydrides of these metalshas required development of specialized, individual processes.

[0006] Hydrides of aluminum with lithium, sodium, and potassium havebeen know for many years. A direct synthesis method to produce thesematerials was first described (French Patent Serial Number 1,235,680).According to Ashby, synthesis of, for instance, NaAlH₄ can be performedby placing either the alkali metal or its hydride into an autoclave withactivated aluminum powder in a solvent such as tetrahydrofuran. Themixture is subjected to hydrogen at a pressure of 2000 psi (about 135atm) and heated to 150° C. for several hours after which the mixture iscooled, the excess aluminum is separated by filtration, and the NaAlH₄isolated by precipitation using a hydrocarbon additive such as tolueneto the tetrahydrofuran solution, followed by vacuum distillation of thetetrahydrofuran. The method is applicable to the production of LiAlH₄,NaAlH₄, KAlH₄ and CsAlH₄.

[0007] Others (Zakharin, et al., Dokl. Akad. Nauk SSR, vol. 1, No. 145,p. 793, 1962; Dvorak, et al. U.S. Pat. Ser. No. 3,357,806; Tranchant, etal. French Patent Serial Numbers 7,020,279 and 6,914,185) developedsimilar processes each of which relied on the use of an organic solvent.

[0008] While alkali-metal based complex hydrides were developed to serveas reducing agents in chemical reactions, other applications of thesehydrides have also been considered in recent years. In particular, thedevelopment of hydrogen as an alternative to fossil fuels has spurredthe search for materials capable of serving as economic sources forhydrogen storage and retrieval. Due to their gravimetric energydensities, hydrides of the alkali metals are very attractive. Most ofthese hydrides undergo decomposition releasing hydrogen at moderatetemperatures (<150° C.).

[0009] However, the alkali metal hydrides prepared in the traditionalmanner act only to irreversibly release hydrogen under moderateconditions. While Bogdanovic, et al., (U.S. Pat. No. 6,106,801) havereported that that the addition of a transition metal compound act as acatalyst to aid in the re-absorption of hydrogen, the kinetics of thissystem have been reported to be slow and unstable. Zaluska, et al.,(U.S. Pat. No. 6,251,349) have reported reversible absorption anddesorption of hydrogen is achieved in complex alkali metal-aluminumhydride compounds prepared by mechanical mixing/milling mixtures of thesimple hydrides without the catalyst reported by Bogdanovic, et al.

SUMMARY OF THE INVENTION

[0010] The present invention provides a totally different method forpreparing alkali metal-aluminum hydrides which is based on simple twostep process. The resulting hydrides exhibit outstanding reversiblehydrogenation properties.

[0011] In accordance with one aspect of the invention there is provideda method of producing an alkali metal-aluminum hydride comprisingmechanically milling powders of a simple alkali metal hydride materialwith a metal and a titanium catalyst compound followed by high pressurehydrogenation at temperatures above about 60° C. The alkali metalhydride is NaH, the metal powder is aluminum, and the titanium catalystcompound is TiCl₃, TiF₃, or a mixture of equal parts of these twocompounds.

[0012] In another aspect of this invention, there is provided a methodof producing an alkali metal-aluminum hydride comprising mechanicallymilling powders of an alkali metal with a metal powder and a titaniumcatalyst compound, wherein the alkali metal is sodium, and the metalpowder is aluminum and the titanium catalyst compound is TiCl₃, TiF₃, ora mixture of equal parts of these two compounds.

[0013] In yet another aspect of this invention, there is provided amethod for preparing an alkali metal-aluminum hydride in a two-stepsolid-state reaction, wherein the first step comprises mechanicalmilling and the second comprises high pressure hydrogenation at elevatedtemperatures.

[0014] In the first step, the method is performed with dry powders ofthe components (i.e., without a solvent or any other suspension aid)under a blanket of a dry inert gas such as argon. The method isaccomplished by subjecting the chosen reagent materials to a mechanicalmilling means, wherein the milling means consists of a ball mill, aplate or impact grinder, a blade, rod or whisk mixer, blender, oragitator.

[0015] In the second step, the method is completed by heating the milledcontents to a temperature of about 100° C., while maintaining a hydrogengas pressure in the container above the equilibrium plateau pressure ofthe reaction, (above about 30 atm hydrogen).

[0016] In yet another aspect of the invention the pressure of hydrogengas is maintained at about 100 atm of hydrogen while heating the milledmixture to an initial temperature of about 125° C.

[0017] In another aspect of the invention there is provided catalystdoped alkali metal-aluminum hydrides which effectively function as arecyclable source/sink for hydrogen gas.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 illustrates the first four hydriding absorption cycles forthe example of NaAlH₄+Na₃AlH₆ made by the process of the presentinvention with the starting of 1.03 moles NaH+1.0 mole Al+0.01 molesTiCl₃.

[0019]FIG. 2 illustrates the first four hydriding desorption cycles forthe example of FIG. 1.

[0020]FIG. 3 illustrates the first three hydriding absorption cycles forthe example of NaAlH₄+Na₃AlH₆ made by the process of the presentinvention with the starting of 1.12 moles NaH+1.0 mole Al+0.04 molesTiF₃..

[0021]FIG. 4 illustrates the first two desorption hydriding cycles forthe example of FIG. 3.

[0022]FIG. 5 illustrates the first four hydriding absorption cycles forthe example of NaAlH₄+Na₃AlH₆ made by the process of the presentinvention with the starting of 1.0 moles NaH+1.0 mole Al+0.02 molesTiCl₃.

[0023]FIG. 6 illustrates the first three desorption hydriding cycles forthe example of FIG. 5.

[0024]FIG. 7 illustrates the first four hydriding absorption cycles forthe example of NaAlH₄+Na₃AlH₆ made by the process of the presentinvention with the starting of 1.0 moles NaH+1.0 mole Al+0.02 molesTiCl₃.

[0025]FIG. 8 illustrates the first three desorption hydriding cycles forthe example of FIG. 7.

[0026]FIG. 9 show Arrhenius plots of the rates of hydrogen desorptionfrom NaH+Al samples that were hydrided after doping with three differentlevels of TiCl₃ or TiF₃ using the direct synthesis method of the presentinvention to prepare NaAlH₄+Na₃AlH₆.

[0027]FIG. 10. Cu Kα X-ray diffraction patterns after hydriding samplesof 1.0Na+1.0Al+0.02TiCl₃ (after 5 hydriding cycles);1.12NaH+1.0Al+0.04TiF₃ (after 4 hydriding cycles); and1.12NaH+1.0Al+0.04TiCl₃ (after 2 hydriding cycles)

DETAILED DESCRIPTION OF THE INVENTION

[0028] The hydrides of alkali metals and aluminum are compounds thatbelong to the larger class of complex hydrides. These compounds areknown to liberate copious amounts of hydrogen either by direct thermaldecomposition or by one-time hydrolysis. However, they were generallyconsidered too irreversible for practical hydrogen storage applications.This was until Bogdanovic, et al., (Bogdanovic and Schwickardi, J.Alloys and Compounds, vol. 253, no. 1, 1997) demonstrated that NaAlH₄,would reversibly desorb and absorbed hydrogen under relatively mildconditions when doped with one of a number of catalyst compounds. Sincethat time there has been a growing body of work in characterizingcatalyzed alkali metal-aluminum hydrides, as well as the development ofnew catalysts and methods of preparation.

[0029] The present invention provides a method for the preparation andproduction of alkali metal-aluminum hydrides. The method is believed tobe general to the hydrides of alkali metals (Li, Na, and K), as well asthe simple hydrides of many of the alkaline earth (for example Mg, Ca,and Ba). Furthermore, it is also believed that aluminum may besubstituted by a transition metal such as, for example, Co, Fe, Mn, Ni,Ti, V, and Zr. The invention, therefore, should not be construed aslimited solely to the production of the alkali metals generally orsodium aluminum hydride specifically.

[0030] The present invention also avoids the problem of solventcontamination, associated with many of the prior art methods forfabricating alkali metal-aluminum hydrides, by providing a simple twostep dry synthesis preparation process. Furthermore, the present methodprovides a means for preparing these materials from either the simplealkali hydrides or directly from the alkali metal itself.

[0031] General Method

[0032] In a particular embodiment, fabrication of alkali metal-aluminumhydrides comprise mixing powders of a simple alkali metal hydride (LiH,NaH, KH) with aluminum powder and a transition metal catalyst compound(typically a titanium catalyst compound such as TiCl₃, TiF₃, or mixturesof equal parts of these materials) in the desired proportion and ballmilling the constituents under an inert atmosphere of argon gas. (Whilenot attempted other dry gas such as helium, hydrogen are also believedto be effective). The milling step is carried out at or near roomtemperature.

[0033] In especially preferred embodiments, fabrication of the alkalimetal-aluminum hydride comprises mixing powders of an alkali metal (Li,Na, and K) with aluminum powder and a transition metal catalyst compound(typically a titanium catalyst compound such as TiCl₃, TiF₃, or mixturesof these materials) in the desired proportion and ball milling theconstituents in an inert atmosphere of argon, for a period of up toabout 2 hours, and then hydrogenating the milled mixture at highpressure while heating the mixture externally to an initial temperatureof about 125° C. to provide a mixture of the stable tetravalent andhexavalent hydride intermetallic phases as follows:Na + Al + 2H₂ ⇔ 1/3Na₃AlH₆ + 2/3Al + H₂ ⇔ Na  AlH₄

[0034] Specific Embodiments

[0035] By way of example, the powders of the present invention aremilled in a high energy ball mill such as are available from SPEXCertiPrep Inc., (203 Norcross Avenue, Metuchen, N.J. 08840). A SPEX™8000 series mixer/miller using tungsten carbide balls and operated at aweight ratio of powders-to-mill balls of about 1:9 was found to besuitable. A single batch of mixed powders comprised about 10 grams ofmaterial per run.

[0036] The powders were milled for a total milling time of 2 hours, atnear room temperature, and under a high purity argon gas atmosphere thatis gettered to remove oxygen contamination. After milling, about 1.5grams of the mixture was transferred (again under an argon atmosphere)to a stainless steel reactor vessel with an internal volume of about 16cm³ and exposed to high purity (99.999%) hydrogen gas pressurized tobetween about 80 atm to about 100 atm while the steel reactor and itscontents are heated externally with electrical tape to about 125° C. forup to 20 hours. Pressure measurements were taken using a calibrated 200atm pressure transducer for the absorption half-cycle and a 1.3 atmcalibrated Baratron™ capacitance manometer for the desorptionhalf-cycle. Data was recorded with a computer.

[0037] Specific examples are provided below in order to better describethe invention.

EXAMPLE 1

[0038] In a first example, the hydrides NaAlH₄+Na₃AlH₆, were produced bycombining 3.25 grams of NaH with 3.55 grams of aluminum metal powder and0.203 grams of a TiCl₃ catalyst precursor compound (molar ratios of1.03:1.0:0.01) and the mixture mechanically milled in a tungsten-carbidelined steel vial with several tungsten-carbide balls in a SPEX™ mill(SPEX™ 8000) packed at a powder-to-ball weight ratio of about 1:9.Excess alkali metal hydride is added to account for the formation ofNaCl during processing. The process was carried out at room temperatureand under an argon atmosphere. The mixture of powders was milled forabout 2 hours. Excess alkali metal hydride was added to account for theformation of NaCl during processing.

[0039] After milling, about 1.5 grams of the mixture (under an argonatmosphere) was transferred to a stainless steel reactor vessel havingan internal volume of about 16 cm³ and exposed to high purity (99.999%)hydrogen gas. The vessel was pressurized with the hydrogen to betweenabout 80 atm and 100 atm after which the steel reactor and its contentswere heated externally, using an electrical tape, to about 125° C.Heating continued for up to 20 hours. Pressure measurements were takenby using a calibrated 200 atm pressure transducer for the absorptionhalf-cycle and a 1.3 atm calibrated Baratron™ capacitance manometer forthe desorption half-cycle. Data was recorded with a computer.

[0040] The initial hydrogenation step is shown in FIG. 1 as the 1^(st)absorption half-cycle (1^(st) absorption) in this Example. FIGS. 1 and 2show the next three absorption/desorption half-cycles. As seen in FIG.1, the sample reaches about 90% of its initial first cycle capacitywithin about 20 hours, after which the rate of hydrogen absorptionimproves to about 5 hours in the subsequent half-cycles. FIG. 2 shows adesorption rate (to about 90% of capacity) occurs within about 2 hours.

EXAMPLE 2

[0041] Fabrication of a second example of the catalyzed hydridesNaAlH₄+Na₃AlH₆ was performed by mechanically milling 1.85 grams of NaHwith 1.86 grams of aluminum metal powder and 0.289 grams of a TiF₃catalyst precursor compound (molar ratios of 1.12:1.0:0.04) in atungsten-carbide lined steel vial with tungsten-carbide balls in a SPEX™mill. Processing was performed as described in Example 1 above; excessalkali metal hydride was added to account for the formation of NaClduring processing.

[0042] Initial hydrogenation is shown in FIG. 3 as the first half-cycle(1^(st) absorption) in this example. Again, the sample reaches about 90%of it maximum capacity within about 20 hours. Subsequentabsorption/desorption half-cycles (2^(nd) and 3^(rd) absorption and1^(st) and 2^(nd) desorption) for this example are shown in FIGS. 3 and4. The rates of each subsequent absorption half-cycle after the initialhalf-cycle are seen to improve from under about an hour for 80% ofmaximum capacity, and to about 5 hours for 90% of capacity. FIG. 4 showsdesorption of hydrogen to about 60% of capacity was achieved withinabout 1 hour and to about 90% of capacity within about 2.2 hours.

[0043] Evidence of the formation of the alkali-metal aluminum hydridesNaAlH₄+Na₃AlH₆ in this example was confirmed by the x-ray diffractionpattern shown in FIG. 10. The pattern was obtained from a portion of thematerial after the 4^(th) hydriding cycle shown in FIG. 4 and isdisplayed as the middle or second of the three spectra shown in FIG. 10.

EXAMPLE 3

[0044] The preparation of the catalyzed hydrides NaAlH₄+Na₃AlH₆ directlyfrom the alkali metal was demonstrated by mechanical milling 3.03 gramsof sodium metal together with 3.56 grams of aluminum metal powder and0.407 grams of a TiCl₃ catalyst precursor compound (molar ratios of1.0:1.0:0.02) in a tungsten-carbide lined steel vial withtungsten-carbide balls in a SPEX™ mill. In this example processingproceeds as before except that the sodium metal is introduced into theball mill as small slivers or pieces of the cut metal. About one tenthof the quantity is fed into the mill at one time and the contents of themill are mechanically “worked” for several minutes before more metal isadded. This is repeated several time until the required quantity ofsodium is introduced into the mill. Again, the ball mass to sample massratio was about 9:1. Total milling time was about 2 to 3 hours andprocessing took place at near room temperature under a high purity argongas atmosphere.

[0045] After milling, the material formed a dark, hard, metallic-lookingmaterial. About 1.5 grams of the sample was transferred (under argon) toa the stainless steel reactor vessel described in Example 1 and exposedto high purity (99.999%) hydrogen gas. The hydrogen was againpressurized to between about 80 atm to about 100 atm while the steelreactor and its contents are heated externally with electrical tape toabout 125° C. for up to 20 hours. Pressure measurements were taken usinga calibrated 200 atm pressure transducer for the absorption half-cycleand a 1.3 atm calibrated Baratron™ capacitance manometer for thedesorption half-cycle. Data was recorded with a computer.

[0046] In the initial absorption half-cycle shown in FIG. 5 (1^(st)absorption) the formation of NaAlH₄ is preceded by the formation of NaHduring the first high temperature excursion at a temperature of about200° C. Subsequent NaAlH₄ formation took place at temperatures between80° C. and 120° C. (100° C. shown). Greater than 90% of the hydrogenabsorption is seen takes place within about a 2 hour period during theinitial hydrogenation step. The results demonstrate that NaAlH₄ can beprepared from Na metal without the need for a separate process toproduce NaH. FIG. 6 shows the material to be fully reversible, releasingabout 2 weight percent hydrogen gas in the desorption half-cycle.

[0047] Evidence for the formation of NaAlH₄+Na₃AlH₆ prepared in thismanner was confirmed by the x-ray diffraction pattern shown in FIG. 10.The spectra was obtained (using an airless sample holder) from a portionof the material after the 5^(th) hydriding cycle and is displayed as thetop (or first) of the three spectra shown in FIG. 10.

EXAMPLE 4

[0048] A final example for the fabrication of NaAlH₄+Na₃AlH₆ wasperformed as in Example 1 to test the effects of a range of catalystcontent on the hydrogenation behavior of the hydride. In this example3.13 grams of NaH was ball milled together with 3.145 grams of aluminummetal powder and 0.720 grams of the TiCl₃ catalyst precursor compound(molar ratios of 1.12:1.0:0.04). Again, milling was preformed in atungsten-carbide lined steel vial with several tungsten-carbide balls.Again, excess alkali metal hydride is added to account for the formationof NaCl during processing.

[0049] Initial hydrogenation is shown in FIG. 7 as the first half-cycle(1^(st) absorption) and is seen to reach about 90% of its initial firstcycle capacity within about 12 hours while FIG. 8 shows initialdesorption to 90% of capacity in about 6 hours.

[0050]FIGS. 7 and 8 show the next two absorption/desorption half-cyclesfor this example. As before the absorption and desorption ratessubstantially improve as due hydrogen capacity. Absorption anddesorption capacity increase from about 3.9 weight percent hydrogen toabout 4.2 weight percent in the last hydriding cycle while rates forabsorption and desorption decrease to 2.5 and 3 hours respectively.

[0051] Evidence of the formation of a quantity of NaAlH₄+Na₃AlH₆ wasagain confirmed by the x-ray diffraction pattern shown in FIG. 10. Thespectra was obtained (using an airless sample holder) from a portion ofthe material after the 2^(nd) hydriding cycle and is displayed as thebottom of the three spectra shown in FIG. 10.

[0052] The foregoing examples, therefore, clearly demonstrates theformation of sodium aluminum hydride. It is believed that lithium andpotassium aluminum hydrides may prepared using a similar technique. Itis demonstrated further, as shown in FIG. 9, that the use of thetitanium catalyst compound, which some have reported to be unnecessary,has a marked and dramatic effect on the rate of hydrogen desorption fromthe sodium aluminum hydrides compounded by the present method. FIG. 9illustrates this effect as multiple Arrhenius plots for several hydridesamples that contain various levels of the titanium catalyst compound.These curves clearly show an increase of several orders of magnitude inthe kinetics of hydrogen desorption by the doped hydride material overthe undoped material and the effect appears to require only a modestamount of the catalyst compound in order to obtain the desired increasein hydrogen transfer rate.

[0053] A new and novel method for the preparation of complex alkalimetal-aluminum hydride compounds that is capable of reversiblehydrogenation has been demonstrated.

We claim:
 1. A method of producing one or more complex hydride compoundscapable of reversible hydrogenation, comprising: mechanically mixing aalkali metal hydride with aluminum powder and a powder of a transitionmetal catalyst compound in order to provide a compounded powder mixture;and hydrogenating said compounded mixture at an elevated temperature andpressure to provide one of more alkali metal-aluminum hydride compounds.2. The method according to claim 1, wherein said alkali metal hydride isselected from the group of hydrides consisting essentially of LiH, NaH,and KH.
 3. The method according to claim 1, wherein said transitionmetal catalyst compound is selected from the group of compoundsconsisting essentially of TiCl₃, TiF₃, and mixtures thereof.
 4. Themethod according to claim 2, wherein the molar ratio of said alkalimetal hydride to said aluminum powder is 1:1 to 4:1.
 5. The methodaccording to claim 3, wherein said molar ratio of the transition metalcatalyst compound to the alkali metal hydride is 1:20 to about 1:100. 6.The method according to claim 1, wherein said step of mechanicallymixing comprises a process selected from the group consisting of ballmilling, plate or impact grinding, and blending, stirring, or agitatingwith or without a mechanical aid.
 7. The method according to claim 6,wherein said step of mechanically mixing comprises ball milling saidalkali hydride and said aluminum powders at a weight ratio of mill ballsto said powders of 30:1 to 12:1 for a time of 0.1 to 10 hours.
 8. Themethod according to claim 1, wherein said step of mechanically mixing iscarried out in an atmosphere consisting essentially of argon.
 9. Themethod according to claim 1, wherein said step of mechanically mixing iscarried out at about room temperature.
 10. The method according to claim1, wherein said step of hydrogenation is performed at an initialtemperature of above about 60° C., and wherein said hydrogen pressure ismaintained above an equilibrium plateau pressure for hydrogen at saidinitial temperature.
 11. The method according to claim 1, wherein saidstep of hydrogenation is performed at an initial temperature about 125°C., and wherein said hydrogen pressure is maintained at about 100atmospheres and for at least about 2 hours.
 12. A method of producingone or more complex hydride compounds capable of reversiblehydrogenation, comprising: mechanically mixing a comminuted form of analkali metal, with aluminum powder and a powder of a transition metalcatalyst compound to provide a compounded mixture; and hydrogenatingsaid compound mixture at an elevated temperature and pressure to providean alkali metal-aluminum hydride compound.
 13. The method according toclaim 12, wherein said alkali metal is selected from the groupconsisting of Li, Na, and K.
 14. The method according to claim 12,wherein said transition metal catalyst compound is selected from thegroup of compounds consisting essentially of TiCl₃, TiF₃, and mixturesthereof.
 15. The method according to claim 13, wherein the molar ratioof the alkali metal to the aluminum is 1:1 to 4:1.
 16. The methodaccording to claim 14, wherein said molar ratio of the transition metalcatalyst compound to the alkali metal is 1:6 to about 1:100.
 17. Themethod according to claim 12, wherein said step of mechanically mixingcomprises a mechanical milling process selected from the groupconsisting of ball milling, plate or impact grinding, and blending,stirring, or agitating with or without a mechanical aid.
 18. The methodaccording to claim 17, wherein said step of mechanically mixingcomprises ball milling said comminuted alkali metal, said aluminum, andsaid transition metal catalyst compound at a weight ratio of mill ballsto said mixed materials of 30:1 to 9:1 for a time of 0.5 to 3 hours. 19.The method according to claim 12, wherein said step of mechanicallymixing is carried out in an atmosphere consisting essentially of argon.20. The method according to claim 12, wherein said step of mechanicallymixing is carried out at about room temperature.
 21. The methodaccording to claim 12, wherein said step of hydrogenation is performedat an initial temperature above about 60° C., and wherein said hydrogenpressure is maintained above an equilibrium plateau pressure forhydrogen at said temperature.
 22. The method according to claim 12,wherein said step of hydrogenation is performed at an initialtemperature of about 125° C., and wherein said hydrogen pressure ismaintained at about 100 atmospheres for at least about 2 hours.
 23. Oneor more complex alkali metal aluminum hydrides produced by the method ofclaim 1, wherein said one or more complex alkali metal aluminum hydridesexhibit reversible hydrogenated and dehydrogenation states.
 24. Ahydride according to claim 23, comprising NaAlH₄ and Na₃AlH₆.
 25. Amethod of providing a source of hydrogen gas comprising: heating aquantity of an alkali metal aluminum hydride or hydrides produced by themethod of claim 12, to provide a supply of hydrogen gas and adehydrogenated form of said alkali metal aluminum hydride; andregenerating said alkali metal aluminum hydride by exposing saiddehydrogenated form of said alkali metal aluminum hydride to source ofhydrogen gas and absorbing said hydrogen gas into said dehydrogenatedform.
 26. A method according to claim 25, wherein said alkali metal isselected from the group consisting of Li, Na, and K.